Cannot create foreign key - laravel-5

Question

I want to create a foreign key that is string from table "stocks" to "rfids".
The two tables are shown below.
stocks table:
Schema::create('stocks', function (Blueprint $table) {
$table->increments('tag_no');
$table->string('stock_type');
$table->string('rfid');
$table->foreign('rfid')->references('RFID_UID')->on('rfids');
$table->integer('user_id')->unsigned();
$table->foreign('user_id')->references('id')->on('users');
$table->timestamps();
});
rfids table:
Schema::create('rfids', function (Blueprint $table) {
$table->increments('id');
$table->string('RFID_UID');
$table->integer('user_id')->unsigned();
$table->foreign('user_id')->references('id')->on('users');
$table->timestamps();
});
When i use php artisan migrate it shows error.
SQLSTATE[HY000]: General error: 1005 Can't create table hardware.#sql-81c_c8 (errno: 150 "Foreign key constraint is incorrectly formed") (SQL: alter table stocks
add constraint stocks_rfid_foreign foreign key (rfid) references rfids (RFID_UID))
Someone help me pls!

Answer 1

The migration order is crucial. You have to create the referenced table (rfids) first.
You can order the migrations by changing the date/time in the filename.

Answer 2

I changed the tables this way:
Schema::create('rfids', function (Blueprint $table) {
$table->increments('id');
$table->string('RFID_UID');
$table->integer('user_id')->unsigned();
$table->foreign('user_id')->references('id')->on('users');
$table->timestamps();
});
Schema::create('stocks', function (Blueprint $table) {
$table->increments('tag_no');
$table->string('stock_type');
$table->string('rfid');
$table->integer('user_id')->unsigned();
$table->foreign('user_id')->references('id')->on('users');
$table->timestamps();
});
Instead of using foreign key i did the following while storing
public function store(Request $request)
{
//
if(Auth::check()){
if (Stock::where('tag_no','=',$request->input('tag_no'))->exists()) {
return back()->withInput()->with('errors', 'Tag number already used!');
}
$rfid_tag = Rfid::where('id',"=",$request->input('tag_no'))->first();
$stock = Stock::create([
'tag_no' => $request->input('tag_no'),
'stock_type' => $request->input('stock_type'),
'species' => $request->input('species'),
'rfid'=>$rfid_tag->RFID_UID,
'user_id' => Auth::user()->id
]);
if($stock){
return redirect()->route('stocks.index', ['stocks'=> $stock->tag_no])
->with('success' , 'Stock created successfully');
}
}
return back()->withInput()->with('errors', 'Error creating new Stock');
}
It works fine for me. But idk if its the right solution.